The ordinary water bed comprises a flat horizontal mattress supporting platform, a mattress retaining frame about and projecting upwardly from the platform and a water-filled bladder-like flotation mattress of flexible plastic film supported atop the platform within and retained by the frame.
The ordinary flotation mattress is characterized by normally flat, horizontal top and bottom walls and vertical side and end walls of thin, polyethelene sheet stock or the like.
The top wall of such mattresses are provided with tubular filler stems to facilitate filling the mattresses with water.
The filler stems are preferably and commonly specially formed so that they are axially collapsible to normally occur below the top plane of the top walls of the mattresses and such that they can be pulled or drawn vertically and out of the mattresses to afford convenient access thereto.
The most common and preferred form of mattress filler stem is normally closed by a screw cap threaded about and overlying the open free end of the stem and by a plug carried by the cap and engaged in the stem. The plug serves to support the portion of the wall of the stem which occurs within and is engaged by the cap
In addition to the foregoing, the ordinary water bed is provided with and includes an electric resistance heater unit which operates to heat and to thereafter maintain the water filled mattress at a desired and predetermined temperature.
Most water bed heaters provided by the prior art have been in the form of flat, horizontal blanket-type heaters and have been arranged in flat engagement with and between the platforms and the bottom walls of the mattresses with which they are related.
The power supply lines for the heaters extend laterally outwardly from between the platforms and mattresses and are thence suitably extended to related control means and/or power sources at the outside of and remote from the bed structures.
One undesirable feature of the above noted forms of heaters resides in the fact that the heaters, while establishing direct heat conducting contact with the mattresses. establishes similar contact with the platforms to conduct much of the heat which is generated by the heaters into the platforms where it serves little useful purpose and is essentially wasted.
Another undesirable feature of the above noted form of heater resides in the fact that their efficient surface area is limited or small with respect to the surface area of the mattresses with which they are related. As a result of the foregoing, such heaters are only capable of heating small areas of the mattresses with which they are related. Distribution of heat throughout the mattresses depends upon circulation or convection currents in the water within the mattresses, which is oftentimes extremely slow and of questionable effectiveness.
Ordinary water bed or flotation mattresses vary in vertical extent or depth from about 4 inches to about 8 inches and are provided in the several plan shapes and sizes in which conventional beds are provided.